God's factory and the goal of maturity.

John 14:30
 30 I will not speak with you much longer, for the prince of this world is coming. He has no hold on me,

These words were spoken by Jesus shortly before his arrest.  He had come to the end of his earthly ministry and was now about to fulfill the Father's requirement of death.  He makes this statement to his disciples and it turns out that this statement gives the greatest insight into the function of the devil and his importance in our own maturity.

The first encounter we know that Jesus had with the devil is when he was tempted.  It was this process that shows us how God matures us.  Consider what the scripture says regarding Jesus' temptation:

Matthew 4:1
Then Jesus was led by the spirit into the desert to be tempted by the devil.

The scripture EXPLICITLY says the it was the Spirit of God that led Jesus into the desert for one single purpose- to be tempted by the devil.  This is essential to understand because it is exactly the same with us.  God from time to time will lead us to be tempted by the devil.  This insight let's us know how God operates in the lives of the believer, but also know that BEFORE the test God caused the following:

Luke 2:52
 52 And Jesus grew in wisdom and stature, and in favor with God and men.

We can learn from these scriptures that God's way of development is to fill us with wisdom and submit us to Satan's temptation to test for weakness.  Temptation is a testing for weakness and this is what Satan was doing to Jesus; he was looking for a weak spot to which he could use to cause Jesus to sin.  James share insight on this truth:

James 1:13-15

13 When tempted, no one should say, God is tempting me. For God cannot be tempted by evil, nor does he tempt anyone; 14 but each one is tempted when, by his own evil desire, he is dragged away and enticed. 15 Then, after desire has conceived, it gives birth to sin; and sin, when it is full-grown, gives birth to death.

This verse shows what Jesus was talking about when he said that Satan 'has no hold on me'.  You are tempted when your OWN evil desire is awakened.  Each of us has sins that easily besets us, and this is WHY believers fall from time to time. These sins are within each one of us and they constitute our 'own evil desire'.  They represent the hold that Satan has on us.  If you struggle with lying then that is the hold to which you are held by Satan.  Jesus had no such evil desires so he could declare that the devil had no hold on him.  

So now we can see the process of salvation and why the bible declares the we are 'being saved'.  When we come to God he teaches us of Jesus (learn of me he says). This learning targets those areas in us that easily beset us, and once we receive the word we are handed over to Satan to be tested.  This process continues until the believer is no longer overcome with the fault but overcomes victoriously the sin.  Satan is therefore essential because God uses him to test us for weakness.  The more we are exposed to the temptation and because of our assimilation of the word of God the less we are susceptible to that particular sin until finally we mature to the point where we are no longer taken by the sin.  The end result of Gods process is:

Ephesians 5:26-27
 26 That he might sanctify and cleanse it with the washing of water by the word, 27 That he might present it to himself a glorious church, not having spot, or wrinkle, or any such thing; but that it should be holy and without blemish.

So my friends I say as Peter:

2 Peter 3:14

14 So then, dear friends, since you are looking forward to this, make every effort to be found spotless, blameless and at peace with him.